//
// experimental/use_coro.hpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2021-2022 Klemens D. Morgenstern
//                         (klemens dot morgenstern at gmx dot net)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef ASIO_EXPERIMENTAL_USE_CORO_HPP
#define ASIO_EXPERIMENTAL_USE_CORO_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include "asio/detail/config.hpp"
#include <optional>
#include "asio/bind_cancellation_slot.hpp"
#include "asio/bind_executor.hpp"
#include "asio/error_code.hpp"
#include "asio/experimental/detail/partial_promise.hpp"

#include "asio/detail/push_options.hpp"

namespace asio {

    class any_io_executor;

    namespace experimental {

/// A completion token that represents the currently executing resumable
/// coroutine.
/**
 * The @c use_coro_t class, with its value @c use_coro, is used to represent an
 * operation that can be awaited by the current resumable coroutine. This
 * completion token may be passed as a handler to an asynchronous operation.
 * For example:
 *
 * @code coro<void> my_coroutine(tcp::socket my_socket)
 * {
 *   std::size_t n = co_await my_socket.async_read_some(buffer, use_coro);
 *   ...
 * } @endcode
 *
 * When used with co_await, the initiating function (@c async_read_some in the
 * above example) suspends the current coroutine. The coroutine is resumed when
 * the asynchronous operation completes, and the result of the operation is
 * returned.
 */
        template<typename Executor = any_io_executor>
        struct use_coro_t {
            /// Default constructor.
            ASIO_CONSTEXPR use_coro_t(
#if defined(ASIO_ENABLE_HANDLER_TRACKING)
# if defined(ASIO_HAS_SOURCE_LOCATION)
                    asio::detail::source_location location =
                      asio::detail::source_location::current()
# endif // defined(ASIO_HAS_SOURCE_LOCATION)
#endif // defined(ASIO_ENABLE_HANDLER_TRACKING)
            )
#if defined(ASIO_ENABLE_HANDLER_TRACKING)
# if defined(ASIO_HAS_SOURCE_LOCATION)
            : file_name_(location.file_name()),
              line_(location.line()),
              function_name_(location.function_name())
# else // defined(ASIO_HAS_SOURCE_LOCATION)
            : file_name_(0),
              line_(0),
              function_name_(0)
# endif // defined(ASIO_HAS_SOURCE_LOCATION)
#endif // defined(ASIO_ENABLE_HANDLER_TRACKING)
            {
            }

            /// Constructor used to specify file name, line, and function name.
            ASIO_CONSTEXPR use_coro_t(const char *file_name,
                                      int line, const char *function_name)
#if defined(ASIO_ENABLE_HANDLER_TRACKING)
            : file_name_(file_name),
              line_(line),
              function_name_(function_name)
#endif // defined(ASIO_ENABLE_HANDLER_TRACKING)
            {
#if !defined(ASIO_ENABLE_HANDLER_TRACKING)
                (void) file_name;
                (void) line;
                (void) function_name;
#endif // !defined(ASIO_ENABLE_HANDLER_TRACKING)
            }

            /// Adapts an executor to add the @c use_coro_t completion token as the
            /// default.
            template<typename InnerExecutor>
            struct executor_with_default : InnerExecutor {
                /// Specify @c use_coro_t as the default completion token type.
                typedef use_coro_t default_completion_token_type;

                /// Construct the adapted executor from the inner executor type.
                template<typename InnerExecutor1>
                executor_with_default(const InnerExecutor1 &ex,
                                      typename constraint<
                                              conditional <
                                              !is_same<InnerExecutor1, executor_with_default>::value,
                                              is_convertible < InnerExecutor1, InnerExecutor>,
                                      false_type

                >::type::value
                >::type = 0)
                ASIO_NOEXCEPT
                        : InnerExecutor(ex)
                        {
                        }
            };

            /// Type alias to adapt an I/O object to use @c use_coro_t as its
            /// default completion token type.
#if defined(ASIO_HAS_ALIAS_TEMPLATES) \
 || defined(GENERATING_DOCUMENTATION)
            template <typename T>
            using as_default_on_t = typename T::template rebind_executor<
                executor_with_default<typename T::executor_type> >::other;
#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
            //   || defined(GENERATING_DOCUMENTATION)

            /// Function helper to adapt an I/O object to use @c use_coro_t as its
            /// default completion token type.
            template<typename T>
            static typename decay<T>::type::template rebind_executor<
                    executor_with_default<typename decay<T>::type::executor_type>
            >::other
            as_default_on(ASIO_MOVE_ARG(T) object) {
                return typename decay<T>::type::template rebind_executor<
                        executor_with_default<typename decay<T>::type::executor_type>
                >::other(ASIO_MOVE_CAST(T)(object));
            }

#if defined(ASIO_ENABLE_HANDLER_TRACKING)
            const char* file_name_;
            int line_;
            const char* function_name_;
#endif // defined(ASIO_ENABLE_HANDLER_TRACKING)
        };

/// A completion token object that represents the currently executing resumable
/// coroutine.
/**
 * See the documentation for asio::use_coro_t for a usage example.
 */
#if defined(GENERATING_DOCUMENTATION)
        constexpr use_coro_t<> use_coro;
#elif defined(ASIO_HAS_CONSTEXPR)
        constexpr use_coro_t<> use_coro(0, 0, 0);
#elif defined(ASIO_MSVC)
        __declspec(selectany) use_coro_t<> use_coro(0, 0, 0);
#endif

    } // namespace experimental
} // namespace asio

#include "asio/detail/pop_options.hpp"

#include "asio/experimental/impl/use_coro.hpp"
#include "asio/experimental/coro.hpp"

#endif // ASIO_EXPERIMENTAL_USE_CORO_HPP
